Grid controlled rectifier tube



June 8, 1948. c. P. SMITH GRID'CONTROLLED RECTIFIER TUBE Filed June 20, 1947 Patented June 8, 1948 UNITED' litt` GRIDfCONTRELED REGTIEIERTUBE Charles P. Smith;l Lancaster, -Pa-,assinontol- Radio Corporationl of America., a corporation.'

of Delaware Application-'June 20;1947, .Serial-No2 7565054^`-V lllClaims.- (Cl. 250"-275')" filament'- Voltage.l and anode; voltage'zis Varied,v

through-.360. degrees; In .tubes-.off this: type; titi is desirable.y to euse; aulamentary cathode? heated..

by: an .A'...C. Yvoltage. circuit... The .lamentary'f' cathode-is enclosed.'withinaheatashield connectedf. electrically to oneendnf.tha.lament.. Alsopthe'. usual-.procedure is. to. make the zgrd: andranolle circuitL returns to :the Llament .transformer center 1 tap... The tube discharge.takesplace:zthroughiant opening` in :theheat sheldzwhi'chidueto .thewariaeA tion of its potential;with;the:appliediAaf-Ctilaey ment' voltage, exerts@J .grid:a'ction,V on;the=start ingicharacteristicof theztubei. Thisffgridactian of the .beati shield.. causes large .-"variationsx im the j amount.v .of. anode. starting voltage nrequiredl.. Moreover,- I have found that.th'esrequire'dtamount of .anode starting Voltagewaries-.Withf a.: changeiin.: the xphase.relationsliiptlrletweenthe,sanctiek voltage.. andf' the flament voltag et It!V is, therefore; an: obj ect:V of: my.: ini/entierr-110;.` provide .an electron discharges device.l of; the.zgasav type-havingimprovedcharacteristics;

ItI is l'also 1anobjectfvcftmyainventiomto; prmfde'1-y al controlled 'gas -tube ehavings atxedanodstartel ingvoltage f onpredeterminedt voltages yimpressed:` cnthe. otherV electrodes.y

It is also 1 an s obj ect` of my invention. tolpitovide: a controlled.v gas-tube in lwhich.: the 1 .gridtaction of the heatfshield is minimized;

The novel\features.Whichlbelieve tobe'charaoe teristic of luy-.invention areset forthiwith 'parel ticularity-v in 1 the appended claims', butxthe invena A tionitself J will ibest; .be understood @by-reference tot thefollowing description.takenin:connectioniwithl the-'accompanying drawing, in which:

F'ig.V 1 is a View# partially` rin ..sectionvof raigas= control tube according,r to myinventiont:

Fig; 2- yis al crossesectional view-rr along.5 sectionalr4 lineaafofFig.` 1; f

Fig. 3 is a schematic-showing fofiascircuit1-a`ppliy cation` incorporating thertube of.- Fig:. 1;-

Eig..v 42 discloses.: the relationshipstnottha anoderz starting-,Voltagefto :the: grid; bias',` voltageazofxgas f control: tubes; and..

ligst,I .6, 7 and.8 .disclose-isectionalfvievvs zof the. several modicationsoftube structure, according. to.my invention.

Fig.. 1 discloses 'a gas, control' tubev havingjan nf electronadischarge v envelope.: Ill. closed .ati oneen'dkbyI a p ress I2." Mounted on this end of the tube isa base Illfhaving@l leads I5 extending. therefrom. Within the envelope l Il;y is.acircularanodeplate I 6` supported by.; rods .I8.`Which are mounted' inca depending;

glass .press 2ll.fromh the top. of the tube envelope. The supporting..rods.. I8Lform. conductor leads fromA thez anode, I6; to 'flexible .leads l I 9"l'e'ading, to the :terminal cap. Z'Illmountedon l the outer Sportion ofthe tube...

Thecathodeelectrode of thistubelcomprises a lamentary element 26. The). cathode filament 26is .preferably-in the formofja corrugated ribbon Which-is:.wound.- to.. form a., spira/1L' arrangement. The.- ilamentspiralljis supported on .-a -ceramic rod t v281.-,With..the :inner edges. ofthe spiral-turns resting-,f on J thetop f of.. the. .ceramic .rod 28T.- The ceramic.- rod 2 .isI in.. turn supported.- horizontally` thef sidefrodsL-t g* and. A32 which .are mounted Y ini-the .glasspress :I 2.L Theends ofthe ilaruentaryy cathode ribbon.. are Irespectively` Welded at.. 34`land 3G-Qtofthecorresponding side ,rods 30fandl32; Side rodsr Ilfand 32-tormtconductive leads f`o1.conr1ect inet. thea-ends of.. the. lamentary cathode.. to an appropriate sourcefof electrical energy. For` this purpose;4 the... side r.ods3|l..ar1dlA 32 are.; connected throughl the.- glasstpress L.l 2.1respectivelyf to. two of the base *.pins I 5. The .surface of. the .corrugated filament ribbon. ff 2li-isn coated with.` an 1 .electron emissive materiaLsuchrasa mixture .of,.fthe.oxides ofv barium Y ariclustroritium,y to ,prot/fidel. a` source of..

electron emission Within..thetube.l=

Surrounding-.- the: catlflodef.` structure 26- is a. l

cylindricalfmetal heatshieldv..spaced therefrom.

The-rheatshield .38 is.` mounted; Acoaxial (with. the circulan anode.y electrodef I6... The. bottom. of. Athe cylindrical shield 33 is closed'by-a-,crcular metal plate--structure` lttsxed at its lperiphery yto.,.the

innen. surface. ofr the. lower.V end.y of. cylinder!V 38...

Bottom fplate 1 4 this.r apertured` to.. permit the pas-v sage: `=therfethrouah. of,- -thefcathode support rods.v 30.- and32.: A: rod42.sea1ed.intthe. glass stem. I 2 extendsI upwardly, yto support thexshield' plate. 4K1. atcitsV-fcentem A,` metaltwasher dtxed. to both.. the frod 42-fa-ndlthefp1ate 4tprovides .afrigid :brace for therfltieat:shielda` Likewiset Va .similar .metal` washer, 44- xedtothe siderod .30 and.sect-tred..inv abutlrnentv totthe:y v bottom. of. plate 40. forms. an .A additional rigid .support forthe heatshield 38;

Throughwasher ,45' shield i38fis .electrically tied totleienddvof the iilamentary cathode; This' places the heat 'shield".38"'at'.the^same potential as the terminalend.34"of the cath'ode26l"l The`- other cathode" support' rod;"32 is' insulatedifrom" platei'by the in'sertionrof' a* ceramic 'washer/465"V The upper end of the heat shield 38 is partially closed by an annular plate element 48 whose periphery is fixed to the inner surface of the cylinder 36. The plate 48 has an opening or p aperture 56 which is coaxial with both the circular The purpose of the closed heat shield 38 is toV prevent the dissipation of heat energy from the lamentary cathode and results in less electrical, e energy being required to raise the temperatureof the cathode to the desired point for electron emission. A second apertured plate 52 may be fixed to the inner surface of the end shield plate 48 to provide greater heat insulation. Furthermore,l i the heat shield 38 is tied electrically to the cath'- ode potential so that theoretically the shield will have a'neutral eiect upon the electron discharge from the cathode 26. n

Between the llamentary cathode 26 and the anode electrode I6 is .mounted a control electrode .1

or grid structure 54. The grid electrode 54 includes a tubular portion 56 Vextending downwards coaxial with the anode plate I6 and aperture 56 in the shield plate 48." The grid structure 54 is mounted on a cylindrical portion 58 extending coaxial to the ,sides of the glass envelope I6. Fixing this grid cylinder 58 within thetube are channel bar side rods 6U which extend adjacent to the stem I2. Mounting the supporting'side rods 66'on the stem tubulation I2 are additional rod supports 62 held rigidly to the stem I2 by a screw type clamp means 63. The control plate 54 and the tubular portion 56 are preferably made of heavy copper material so as to proy vide high heatv conductivity from the region of the tubular portion 56 to cylindrical grid portion 63. This grid structure 58 operatesas a radiator or heat dissipating means for lowering the operi ative temperature of the control grid. To further increase the radiating surface of the grid I cylinder 58, it is preferably coated with `powdered zirconium metal sintered to the Vmetal surface of cylinder 58. With this arrangement, the heat encountered in the region of the arc discharge within the ktubular portion 56 is eiectively connected to the radiating cylinder 58 and appropriately dissipated. This means permits the control grid 54 to operate at a lower temper-v ature and helps to eliminate the undesirable effects of grid emission. Spring centering clips 6d are fixed to side rods 60 to keep the gridl structure properly spaced from the sidewalls of the tube envelope. Y

Fig. 3 illustrates an application of this type of control tube and also shows one manner in which the tube parts are connected in an operative circuit. In this gure, the 'gas control tube I0 is used to operate a relay, for example, at a predetermined time when thereis a scheduled change of grid potential. A source of electrical energy includingfor example, ,av plate circuit transformer 16 provides an alternating potential to circuit lines 12 and 14. Anode plate I6 of the control tube I6 is connected directly to circuit line 12 through a. load or relay 15. The lamentary cathode 26 of tube I0 is heated by a current derived from the secondary 80 of a lament transformer 18. The primary coil'16 of transformer. 18- is connected acrossA the circuit lines 12v and 1-4. Also, the Iilamentary cathode 26 is connected into the alternating circuit by a lead grid 85 joining the center tap of the lament transformer coil 88 with a terminal point 84. The terminal point 84 is separated from circuit line 12 by a large resistance 32 and from circuit line 14 by a much smaller resistance 83. This arrangement produces a greater IR drop between terminal point 84 and circuit line 12 `than between terminal point 84 and line 14. Control grid 54 of the control tube I6 is connected through a Agrid resistance 96 and an adjustable contact 98 to resistance 83. A phototube 66 has its anode electrode 92 joined to circuit line 12 and the photocathode S4 connected directly tothe grid circuit. y'

This circuit arrangement produces a dilerence of potential between the anode I6 of tube II) and the lamentary 'cathode 26. When the anode I6 is positive during the one-half cycle of voltage alternation, the control electrode 54 is at a lower negative voltage potential than the cathode 26. Thecontact 98 inthe grid circuit may bevaried to maintain a sufciently negative potential on grid 54 to prevent the negative cathode 26 and the positive anode plate I6. When there is an activation of the photocathode 94 of phototube 90, the'electron emission from the photocathode 94 will cause a shift of the potential on the control grid 54 of tube II) in the positive direction. Adjustmentsr manner so that the primary emission from the cathode 26 is greatly amplified. This reaction results in a current being conducted through the control tube I6' to operate relay 15.. Y n

The operation of the grid controlled gasv tube I0 is suoli` that the tube will conduct during all of the half cycle whenV the anode is positive,if there is no negativeV chargeon the control grid. If the control grid is maintained at a certain negative value, no discharge will take j place r through the tube during the half cycle the'anode is positive until the voltage drop between the anode and cathode has built up to a critical value.

At this value,v the restraining field of the negar tive control electrode is overcome and the tube will' break down and conduct forthe rest of the half cycle. The tube discharge cannot be stopped by the control grid once it has started. However,

removal of the positive anode potential at the'` end' of the half cycle stops tube discharge.

"If a potential morenegative than a determinable critical value is applied to'thecontrol grid, no discharge will take place through the tube under normalL operating conditions.4

prevent the tube from discharging. If" the grid potential is shifted to a point in the positivedirection above the critical value by any meansy such as the phototubeill of Fig. 3, the Vcontrol tube willconduct when the potential difference f between the anode and cathode electrodes reaches is electrically connectedto one end 34 of' the cathode filament 26, the heat shieldvarie's froml a positive maximum to a negative maximum and back.' as the A.C. filament voltage varies through any electron discharge between In usual practice a bias potential is placed on'the con:` trol grid more negative than the critical value to of. a discharge between saidanode and cathode electrodes, means electrically connecting said cathode electrode and said heat shield in the Y path of the discharge, said electrostatic shield means connected to the other one of said cathode portions to electrostatically neutralize said aper-` tured heat shield. V

2. An electron discharge device comprising a sealed, envelope, an anode electrode mounted within said envelope, a cathode electrode spaced within said envelope from said anode electrode, said cathode electrode l'including a filament, a metal lead connected to each end of. said filament for conducting a heating current thereto, a shield spaced within said envelope from said cathode electrode and including a portion ex,- tending between said anode and cathode electrodes, said shield portion having an aperture for the passage of a discharge between said anode and cathode electrodes, means electrically connecting said shield to one of saidmetal leads, a shield electrode mounted in the path of said discharge and between said cathode electrode and said shield portion, said shield electrode connected to the other one of said' metal leads to electrostatically neutralize said apertured shield portion. Y

3. An electron discharge device comprising a sealed envelope, a gaseous medium within said envelope, an anode electrode mounted within said envelope, a lamentary cathode electrode spaced within said envelope from said anode electrode, a conductor lead connected to each end of said filamentary cathode for supplying a heating current thereto, a heat shield within said envelope spaced from and enclosing said cathode, Y

said heat shield having an apertured plate portion for the passage of an arc discharge between saidv anode and cathode electrodes, said heat shield electrically connected to one of said conductor leads,A a foraminous shield `electrode mounted between said cathode electrode and said apertured plate portion in the path of said arc discharge, said shield electrode connected to the other of said conductor leads to electrostatically neutralize said apertured plate portion.

4. AAn electronv discharge devicevcornprising a sealed envelope, a gaseous' medium within said envelope, an anode electrode mounted within saidfenvelope, a cathode electrode including a filament'and a coatingof high electron emissivity fixed to said filament surface to provide a source of electron emission, means connected to the ends of said lament for supplying aheating current thereto, a tubular heat shield within said envelope spaced from .andenclosing said cathode, an annular plate closing one end of said heat shield for the passage ofan arc discharge between said anode and cathode elec# trodes, means electrically connecting vsaid an-v plate to one end of said cathode iilament,V

nular an electrostatic shield electrode having an aperture axially aligned with said annular platey and positioned between said cathode filament and said annular plate, means electrically connecting said electrostatic shield electrode to the other end of said cathode filament static effects of said annular plate upon the electron emission from said cathode are neu-Ay tralized.

5. An electron discharge sealed envelope, a gaseous medium within said envelope, an anode electrodemounted.Withnsaid whereby VelectrodeviceA comprisingf a`A envelope, ya cathode lament including an elec. means connectedlto the ends of said iilament ,to supplya'heating current tron emissive coating,

thereto, alclosed -cylindricalheat shield within said envelope spaced from andenclosing said end of said cathode filament, an electrostatic -shield electrode mounted within said heat shield,

said electrostatic `shield including an f-apertured disc axially aligned with said circular opening,

means electrically connecting said electrostatic shield to the other end of said cathode lament whereby any electrostatic opening upon the electron emission from said cathode are neutralized by said apertured disc.

sealedrenvelope, a gaseous medium within said envelope, an anode electrode mounted within saidk envelope, a cathode electrode spaced within said envelope from said anode electrode, a grid electrode mounted between said anode and cathode electrodes for controlling the initiation of an arc discharge therebetweemwsaid cathode electrode including a filament andan electron emissivev coating on said filament surface, `means for connecting the ends of said cathode iilament to a source of alternating current, a cylindricalheat shield axially aligned with said anode andv control electrodes and enclosing said cathode elec'- trode, a-plate structure closing they end of said cylindrical shield between said cathode and grid control electrodes, said plate structure having a circulary aperture coaxial with said cylindricall shield-for the passage of an arc discharge be-V tween said anode and cathode electrodes, means electrically connecting said heat shield to one end of said cathode filament, an electrostatic shield mounted within said cylindrical shield, said electrostatic shield including a metal ring coaxially spaced between said circular `aperture and said cathode lament, means electrically connecting said electrostatic shield ring to the other end of said cathode filament toneutralize the electrostatic effectsof said circular aperture upon cathode emission whereby the loss of grid electrode lcontrol is prevented.

7. An electron-discharge device having an envelope containing a gaseous atmosphere, an an.

ode electrode within said envelope, an elongated cathode within said envelope, a conducting shield surrounding said cathode, said shield having an aperturetherein through which a discharge can occur -between said cathode and said anode, one end oi said cathode being connected to said shield, an electrostatic shielding means adjacent said aperture, said electrostatic shielding means being connected to the other end of said cathode.

8. An electron discharge device having an envelope containing a gaseous atmosphere, an anode electrode within said envelope, a cathode lament within said envelope, a metallic; shield surrounding said cathode ior shielding said cathode, said shield having an aperture therein through which a dischargecan occur between said'cathode and said anode, one end of said cathode be,-

ing connected to said shield, an electrostatic shielding means within said shield adjacent said aperture, said electrostatic shieldingrmeans being connected to the other end of said Cathode.

9. An electron discharge device having-,an en-r velope containing a gasemismedium.,acatliude.`V

eiects of said circular v 6. An electron discharge device comprisinga Within said envelope and an anode, said cathode including a lament, a heat shield surrounding said filament and having an aperture through which a gas discharge can take place, one side of said lament being connected to said heat shield, and an electrostatic shield Within said heat shield adjacent said aperture and connected to the other end of said filament.

10. An electron discharge device having an envelope containing a gaseous medium, la cathode Within said envelope and an anode, said cathode including a filament, a heat shield surrounding said lament and having an aperture through which a gas discharge can take place between said anode and cathode electrodes, a grid electrode mounted between said anode electrode and heat shield for controlling the initiation of the gas discharge through said aperture, one side of said lament being connected to said heat shield, and an electrostatic shield Within said heat shield adjacent said aperture and connected to the other end of said filament, to neutralize the electrostatic eifects of said shield aperture upon tube discharge whereby loss of grid electrode control is prevented.

CHARLES P. SMITH. 

